Known in the art are percussion devices (cf. British patent specification No. 1170167, publ. Mar. 14, 1967), comprising a casing, a striker accommodated in the casing for reciprocations under the action of fluid under pressure and a fluid distribution system enabling the reciprocations of the striker and causing the striker to impart blows to the casing either toward the front- end part of the casing (forward movement function) or toward the rear-end part of the casing (rearward movement function).
The distribution of fluid under pressure for both functions of the device is controlled by a control member which is movably coupled to the striker. The control member may be installed in two positions with respect to the casing - in the front- end or in the rear-end position, the control member controlling the distribution of fluid under pressure to enable the forward movement function when in one position and controlling the distribution of fluid under pressure to enable the rearward movement function when in the other position.
The control member is coupled to the casing by means of a tube communicating with a source of fluid under pressure, having a helical groove cooperating with a helical groove of a flange attached to the casing. Fluid under pressure is fed to the tube by means of a flexible conduit connected to the tube.
Two pairs of stops are provided on the tube and flange to limit the displacement of the control member when the tube rotates in the flange. The tube is caused to rotate in the flange by imparting rotary motion to the flexible conduit.
The flexible tube should be rotated to bring the control member to the position enabling the forward movement function of the device. The tube is thus caused to move together with the control member to the front-end position until the engagement of the front-end stops of the tube and flange. Upon the admission of fluid under pressure the striker starts reciprocating in the casing and imparting blows thereto which are directed toward the front-end (head) part of the casing, and the entire device moves through the soil leaving a hole therebehind.
To switch the device over for rearward movement function (reversal), fluid under pressure should be shut-off. Then the flexible conduit should be rotated in the opposite direction. The control member is thus caused to move together with the tube toward the rear-end position owing to the provision of helical grooves on the tube and flange until the rear-end stops of the tube and flange engage one another; in this position the control member enables reciprocations of the striker in the casing so as to impart blows thereto in the direction toward the rear-end (tail) part of the casing, and the entire device is caused to move under the action of such blows in the opposite direction through the hole, that is the device works in the rearward movement function.
For switching the device over back for the forward movement function, the control member should be moved back to the front-end position as described above.
The above-described devices are characterized by difficulties encountered in reversing, because with considerable length of a hole and flexible conduit and with an unstable hole (when driving holes in loose soils) the transmission of rotary motion to the tube through the flexible conduit is extremely difficult. The helical grooves of the tube and flange may also be clogged to result in jamming and this also hampers the reversal.
Still another feature of known devices is associated with failure to maintain the pre-set function, that is with the possibility of self-reversal. This is due to the absence of a reliable latching of the control member relative to the casing in each working position since the stops of the tube and flange can lock the tube and hence the control member in one direction only so that upon turning motions of the flexible conduit during operation of the debice (which may be the case if the flexible conduit has hot been straightened beforehands) the tube and the control member associated therewith may take the other position, and the device will be reversed, that is the function will be changed.
The prior art devices are not convenient in operation in that one must make it certain which of the two functions is pre-set in the device before each starting (e.g., by making a test starting). Thus, after the device leaves the hole it should be switched over from the rearward movement function to the forward movement function so as to prepare for a new starting. In addition, the control member may take an intermediate position between the forward and the rearward movement positions (e.g., during transportation).
Known in the art are reversible percussion devices (cf. German patent No. 2340751, publ. Aug. 11, 1973), comprising a casing, a striker installed in the casing for reciprocations under the action of fluid under pressure and a fluid distribution system enabling the reciprocations of the striker so as to impart blows to the casing which are directed either toward the front-end (head) part of the casing for the forward movement function of the device or toward the rear-end (tail) part of the casing for the rearward movement function of the device.
The distribution of fluid under pressure for both functions of the device is controlled by means of a control member which is movably coupled to the striker.
The control member may be locked in two positions with respect to the casing: in the front-end and in the rear-end positions, the control member controlling the distribution of fluid under pressure to enable the forward movement function when in one (front-end) position and controlling the distribution of fluid under pressure to enable the rearward movement function when in the other (rear-end) position.
The control member is coupled to the casing by means of a tube connected to a flange. The flange is rigidly secured to the casing. Fluid under pressure is fed to the tube by means of a flexible conduit connected thereto. The control member is locked in one of two positions with respect to the casing by means of two pairs of stops provided on the tube and alternatively engaging the flange and by means of a spring-biased ball locking member which is installed in the flange and coupled to a control rope. The flange also has longitudinal grooves for receiving the tube stops.
To install the control member in the front-end position so as to enable operation of the device with the forward movement function, the control rope should be pulled so as to release the locking ball from a seat of the tube.
To switch the device over for the rearward movement (reversed) function, the supply of fluid under pressure should be interrupted. The locking ball should be released from its seat by pulling the control rope. The tube is then caused to rotate at a certain angle by turning the flexible conduit so that the tube stops be positioned opposite to the flange grooves. Subsequently the flexible conduit is pulled without removing the pulling force from the control rope, thereby to move the tube axially in such a manner that the front-end pair of stops of the tube should now be on the opposite side of the flange, and the tube is then turned at a certain angle again so that the locking ball should be opposite to its seat in the tube. When the pulling force is removed from the control rope, the ball locks the tube between the front-end pair of stops (and also locks the control member) with respect to the flange and casing. Upon feeding fluid under pressure to the device the striker reciprocates in the casing to impart blows thereto in the direction toward its rear-end (tail) part, and the entire device will move backward through the driven hole, that is the rearward movement function is obtained.
To switch the device over back for the forward movement function, the control member should be moved back to the front-end position as described above.
The above-described devices are characterized in that, in addition to a complicate structure, the reversal is not convenient and reliable since several operations should be made simultaneously with the control rope (pulling) and flexible conduit (turning and pulling). This is not easy and convenient for one operator to do. In addition, it is very difficult if possible to turn the flexible conduit in driving long holes in loose or unstable soils.
The above-described devices also do not have a mechanism for automatically bringing the control member to a position corresponding to the forward movement function. Thus manipulations for switching the device over for the forward movement function should be made before each starting of the device.
In addition, all such devices do not make it possible to change from the rearward movement function to the forward movement function (e.g., under emergency conditions). In order to make such change, the tube shoulds be caused to move axially forward. This cannot be done when dealing with a flexible conduit.